1. Field of the Invention
The present invention relates to a sound field effect control apparatus and a sound field effect control method which apply sound field effects to multichannel audio source signals.
2. Prior Art
To simulate various acoustic spaces such as halls and churches, there have used field effect control apparatuses which apply sound field effects to audio source signals to be reproduced. In recent years, sound field effect control apparatuses have been proposed to apply sound field effects to multichannel audio source signals as the audio source signals.
Important factors that characterize an actual acoustic space include initial reflected sounds and reverberant sounds. The initial reflected sounds are generated by reflection of sound emitted from a sound source by walls of the acoustic space and delivered to the listeners ears. Therefore, the direction, intensity or the like of the initial reflected sounds reflect the position of generation of the original sound in the acoustic space more faithfully than the reverberant sounds.
The conventional sound field effect control apparatuses for applying sound field effects to multichannel audio source signals are, however, constructed so as to apply sound field effects by synthesizing the audio source signals into a monaural source signal, then subjecting the monaural source signal to operations of delay and multiplication by coefficient(s) to obtain a reflected sound signal, and reproducing the obtained reflected sound signal which is monaural by a plurality of loudspeakers. According to this method, information related to the sound source position that was possessed by the original multichannel audio source signals is lost by the synthesization of the audio source signals into the monaural source signal, and therefore the resulting initial reflected sounds each do not have a direction and intensity determined by the position of the sound source.
It is therefore an object of the present invention to provide a sound field effect control apparatus and and a sound field effect control method which are capable of enabling a listener to listen to reflected sounds close to initial reflected sounds generated in an actual acoustic space, by utilizing information reflecting the position of a sound source possessed by multichannel audio source signals.
To attain the above object, the present invention provides a sound field effect control apparatus for applying sound field effects to multichannel audio source signals that are input to the sound field effect control apparatus, the multichannel audio source signals causing sound generated from an imaginary sound source at a predetermined position to be heard by a listener when converted into sound and generated by a plurality of loudspeakers, the apparatus comprising an initial reflected sound generating device that generates multichannel initial reflected sound signals corresponding to initial reflected sounds that will be heard by the listener when the sound is generated from the imaginary sound source at the predetermined position in a predetermined acoustic space, from the multichannel audio source signals.
In a preferred form of the present invention, the initial reflected sound generating device comprises a plurality of initial reflected sound generating devices that generate the multichannel initial reflected sound signals corresponding, respectively, to a plurality of predetermined positions of the imaginary sound source, from the multichannel audio source signals, and a control device that selects one of the plurality of initial reflected sound generating devices according to a selected one of the plurality of predetermined positions of the imaginary sound source, and causes the selected one initial reflected sound generating device to create the multichannel initial reflected sound signals.
Further, in a preferred form of the present invention, the initial reflected sound generating device comprises a plurality of signal processing circuits each connected between one of a plurality of first signal lines through which respective ones of the multichannel audio source signals are input, and a plurality of second signal lines through which respective ones of the multichannel initial reflected sound signals are output.
A concrete example of the initial reflected sound generating device comprises a plurality of delay circuits that delay respective ones of the multichannel audio source signals, a plurality of multipliers that multiplies respective ones of the multichannel audio source signals which are delayed by the delay circuits by predetermined coefficients, and a plurality of adders that add respective ones of a plurality of predetermined combinations of output signals from the multipliers and output results of the addition as the multichannel initial reflected sound signals.
Preferably, multichannel audio source signals correspond to respective ones of the plurality of loudspeakers, and are each created based upon a first transmission function of a signal Transmission path extending from the imaginary sound source at the predetermined position to ears of the listener, a second transmission function of a signal transmission path extending from the imaginary sound source at the predetermined position to a corresponding one of the plurality of loudspeakers, and a third transmission function of a signal transmission path extending from the corresponding one of the plurality of loudspeakers, and the initial reflected sound generating part creates the multichannel initial reflected sound signals by subjecting the multichannel audio source signals to signal processing based upon a fourth transmission function forming a transmission function of a signal transmission path extending from the imaginary sound source at the predetermined position to the ears of the listener, and the second transmission function.
To attain the above object, the present invention further provides a sound field effect control method for receiving multichannel audio source signals and applying sound field effects to the multichannel audio source signals that are input, the multichannel audio source signals causing sound generated from an imaginary sound source at a predetermined position to be heard by a listener when converted into sound and generated by a plurality of loudspeakers, the method comprising an initial reflected sound generating step of generating multichannel initial reflected sound signals corresponding to initial reflected sounds that will be heard by the listener when the sound is generated from the imaginary sound source at the predetermined position in a predetermined acoustic space, from the multichannel audio source signals.
The above and other objects, feature, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.